This invention relates to subsonic wind tunnels used for low speed aerodynamic and automotive testing and, more particularly, to an apparatus for attaining flow conditions within the test sections that are free of disturbances caused by the walls.
Current practice in designing automotive wind tunnels is to size the test section cross-sectional area to be nominally twenty times larger than the frontal area of the typical test vehicle. This sizing is necessary because the finite lateral extent of the wind tunnel flow generally results in deviations of the local flow over the vehicle, relative to that which would occur on the road. These deviations become unacceptably large if the tunnel walls are too close to the vehicle. However, if the test section walls were modified so that streamlines close to the wall were similar to those occurring on the road, then the test vehicle would be in an environment free of wall interference.
Kroeger, et al U.S. Pat. No. 3,552,202 attempts to attain the desired streamlines by providing transverse louvers which permit inflow at the test section boundary, but requires complex apparatus to achieve the effective outflow which is necessary for application to automotive testing. Other art for generating desired air speeds in two-dimensional flow is well known, supersonic wind tunnel nozzle contours being the most common example.